For hydraulic cylinders, the damping effect is obtained by utilizing flow restriction through orifices in the bypass between the chambers. The electro-hydraulic actuator control is enabled by an inherently safe mode valve. When a voltage is applied to the valve no damping effort is generated. When the voltage is released or in case of failure, the valve mode switches to damping mode under operation of a spring making the fluid pass through the restriction.
Known methods of damping of moving aerodynamic surfaces in mechanical or electromechanical devices such as motors or actuators etc. often require the use of additional, and often, complex, electronic circuitry, which can complicate a device.
Damping in mechanical or electromechanical devices having moving aerodynamic surfaces is mandatory to prevent catastrophic flutter oscillations in case of actuator or power supply failure or loss of control. For an electromechanical actuator, this damping effect is provided by generating a reverse torque that is proportional to the position rate of the actuator.
US 2012/0038302 A1 aims to provide a damping solution that can be used in a motor power supply circuit for powering an electric motor that may be used, for example, for actuating a movable air foil of an aircraft. In such situations, two electric motors and two power supplies are connected to the airfoil and are used in a redundant scheme such that in the event of one of the motors failing, the other motor can be used as a replacement. The power supply circuit described in this document comprises an active mode, in which it powers the motor, and a passive mode, in which it provides damping by switching the motor phases across a bank of three damping resistors. The design is based on naturally closed power switching devices so that when the power supply circuit is in active mode, no current flows through the damping resistors while, when the power supply is lost, the windings of the motor are connected to the damping resistors.
US 2011/0254394 A1 describes a supplemental damping effect for an electric motor that is described as being analogous to the damping resulting from the use of a hydraulic cylinder, however, in contrast to what is achieved for a hydraulic cylinder, the damping effect is always available in all circumstances, without the intervention of any device. The damping effect described in this document filters out vibrations originating directly from the mechanism maneuvered by the electric motor. The electric motor consists of a rotor fitted with permanent magnets and comprises a stator, the stator of which is made up of two parts: a stack of laminations forming round teeth and a solid tube-shaped field frame made of a material of the stainless steel kind, enveloping the stack of laminations. The stainless steel constitutes a poor magnetic circuit, with losses through eddy currents and hysteresis. These losses therefore offer braking and damping.